Radio receiving apparatus



July 7, 1931. P. D. LOWELL 1,813,180

RADIO RECEIVING APPARATUS Filed July 16. 1927 "fl Ir- I IN VENT 0R mwLlLPatented July 7, 1931" UNITED STATES" PATENT OFFICE,

v PERCIVAL'D. LOWELL, OF JAMAICA, NEW YORK, ASSIGNOR TO A; H. GREBE &CO., INC.,

OF' RICHMOND HILL, NEW YOBKQA CORPORATION OF NEW YORK RADIO REGEIVINGAPPARATUS Application filed irui 16,1

The present invention relates generally to certain improvements in radiobroadcast receivers and more particularly to means for improving thestabilityand frequency range 1 whichit is the purpose of this inventionto overcome. I v

In the drawings, Fig. '1 represents one unit of a radio frequencyamplifier, using the triode T, with its filament F, plate P and grid G.The input circuit of the triode consists of the coil L and variablecondenser C In the plate circuit of the triode, there is contained thecoil L which will generally be magnetically coupled to the input circuitof another triode. The coil L will generally be magnetically coupled toan antenna circuit.

Fig. 2 shows a slight modification of the arrangement of Fig. 1; theelectrical action is practically the same as that of Fig. 1, but themechanical arrangement of the parts is sometimes more convenient.

Figs. 3 and 4' show alternatives for the arrangement of Fig. 2;.theyare, electrically equivalent but permit a slight'mechanical advantage insome'wiring schemes. 7

Referring to Fig. 1, my inventive'idea is exemplifiedin the arrangementof the connection between the input circuit L C and the grid-filamentelements of the triode. In-

stead of connecting the tunedji'nput circuitto the grid directly thereis arranged between theinput circuit and grid the combination of tworesistances B1 and R and a condenser C The effect of this arrangement istwo-fold; itresults in a wider' frequency range for the circuit thandoes the ordinary connection and i it produces stabilization of theamplifying 1927. Serial No. 206,168.

ment is to. reduce and stabilize the regenerative effect of the triode.acting through the grid platecapacity. v This stabilizing action isaccomplished by the' combined action .of the tworesistances j R and Rand the condenser C The proper proportioning of. these resistances andcapacity depend upon the characteristics of the triode and the frequencyrange the set is designed to cover. It also depends somewhat upon thetypes of coils and condensers used for L and C arrangement increases thefrequency range of the set by decreasing the effect of the'gridfilamentcapacity of the triode upon the tuning-of the circuit L -G Althoughsmall, this triode capacity has a comparatively 7 large effect upon thehighest frequency to w" which the L C circuit can be tuned, because atthe highest frequency the capacity of con-I denser C is adjusted for itslowest value. Now this input circuit (grid-filamentfof the triode isgenerally in'parallel with'condenser, 7 1

C and will thus effectively limit the minimum value of capacity in thetuned, circuit. 1

In. my arrangement the condenser C is in series with the grid-filamentcapacity of the I triode.- As the capacity of two condensers in seriesis less than that of one aloneythis arrangement of condenser Cmaterially reduces the tuning effect of thegrid-filament capacity of thetriodeandmakes it possibleto tune to hi herffrequencies. I I hereas Ihave shown, in Fig. 1, the com: binati'on' circuit, .(Rg in series withthe parallel icombinationyof R and O connected directly between the gridG of the triode anclthe' tunedcircuit L G it will be appreciated bythose skilled in the art that an equivalent arrangement might beobtained by: interchanging'the relative positions of, the biasingbattery B and the combination circuit; v Whereas such an arrangementwould operate inmuch the same manner-as that'shown my drawings, it hascertain objecticnablercharacteristics due to the stray capacities of thecircuit.

,will furthermore be. appreciated by those'skilled in the art that thecombination In addition to producing stabilizationthis.

circuit (R C R might be put directly in series with the biasing batteryB and this arrangement be inserted between points NGr of the circuit orpoints MO of the circuit, or the battery B may be dispensed withaltogether and the resistance R be left between points NG, and the C Rcircuit be placed between N and G. All of these a'rrangements willfunction in much the same manner, some being preferable to othersbecause of the effects of stray capacities inthe circuit.

It will be further understood that the resistances R and It may possiblybe fractional parts of the same physical resistance unit although I havenot found this arrangement as satisfactory as that utilizing twodifferent resistance units. It will be further appreciated that whereasI have shown the condenser C as a physical entity, apart from theresistance R it is possible to so construct the resistance R to obtainthe capacity C inherent in the structure of R Such a scheme I have notfound as useful as the one shown in my drawings where an actualcondenser is shown for C It may be necessary to use different values ofC for different tubes and circuit conditions; whereas it is diflicult tochange inherent capacities an actual condenser C may have its capacitychanged at will.

Another embodiment of my invention is shown in Fig. 2, in which I usethe same elements as for Fig. 1, but dispose them in a somewhatdifferent manner. The resistance R and the condenser C are arrangedbetween the tuned input circuit and the grid as in Fig. 1, but theresistance R I place between the grid and filament circuit. In serieswith this resistance R I may or may not use a suitable biasing batteryfor adjusting the average grid potential; the arrangement of Fig. 1 mayalso be used with or without the biasing battery as desired. The circuitmodification as given in Fig. 2 functions in practically the same manneras does Fig. 1, but the mechanical assembly of the parts is sometimesmore convenient.

In Figs. 3 and i, I have shown slight modi fications of the arrangementof Fig. 2; the electrical operation is essentially the same as that ofFig. 2 but the mechanical arrangement of the connections is sometimesmore convenient.

Although it will be understood that I do not intend to limit myself toany particular values of resistances and capacity, for the guidance ofthose who endeavor to carry out the ideas of this invention, I havefound that with the arrangement of Fig. 1 and with the ordinary triodesin use today as amplifiers suitable values are three megohms for R 1000ohms for R and 25 micro-microfarads for C The words triode, audion,etc., as used herein, are to be understood only as convenientidentifying terms for any multi-electrode vacuum tubes that it may befound desirable to employ and not as an intended limita-tion to theordinary three electrode tubes which have heretofore been extensivelyused.

Having thus described my invention, what I claim is:

1. In a radio frequency amplifier using a triode vacuum tube, thecombination of a tuned input circuit, an inductively reactive platecircuit, two resistances in series between the grid. and tuned inputcircuit, and means for paralleling part of such resistance by a capacitypath.

2. In a tuned radio frequency amplifier the combination of' an audion, atuned input circuit, an inductive plate. circuit, requisite resistancein series with the lead connecting the grid of the audion to the tunedinput circuit and means for paralleling part of such resistance by acapacity path.

3. In a tuned radio frequency amplifier, the combination of an audion, atuned input circuit, an inductive plate circuit and two IGSiStZLIlCGS inseries between the grid of the audion and the tuned input circuit, oneof said resistances being so constructed as to provide an inherentcapacity sufficiently great that the current through the capacity isgreater than the current through the resistance.

4. In a tuned radio frequency amplifier utilizing an audion, means forimproving the stability and frequency range ofthe amplifier, said meanscomprising requisite resistance and a condenser in the grid lead, saidresistance and condenser being associated to cooperate with each other,and said condenser having a capacity of approximately the same value asthat of the input circuit of the audion.

5. The combination of a triode, having a coil in its plate circuit and atuned input circuit connected to the grid-filament terminals,resistances in series with the grid lead, said resistances being in partshunted by a condenser of capacity substantially the same as that of theinput circuit of the triode.

6. A radio frequency amplifier utilizing a triode, having a tunedcircuit connected to the grid and filament terminals, and a coilconnected in the plate circuit, resistances con-' nected between theinput circuit of the triode and tuned input circuit, said resistancebeing shunted in part by a condenser of capacity substantially the sameas that of the input circuit of the triode.

PERCIVAL D. LOWELL.

